One of important things in requirements of a next generation wireless access system should support a demand of a high data transmission rate. To this end, various technologies such as multiple input multiple output (MIMO), cooperative multiple point transmission (CoMP), and relay have been studied.
A wireless access system of the related art has considered one carrier only even though bandwidths between an uplink and a downlink are configured to be different from each other. For example, a wireless communication system of which uplink and downlink respectively have a single carrier and uplink bandwidth is generally symmetrical with a downlink bandwidth has been provided.
However, in order to obtain a broad bandwidth for satisfying a demand of a higher data transmission rate considering that frequency resources reach a saturated condition, the wireless access system has been designed to satisfy basic requirements, which allow each of the bandwidths to operate its independent system, and has introduced carrier aggregation (CA) that groups a plurality of bandwidths in one system.
In this case, a carrier of a bandwidth unit that enables independent operation may be referred to as a component carrier (CC). In order to support transmission capacity which is increased, the recent 3GPP LTE-A or 802.16m system has extended a bandwidth to reach 20 MHz or more. In this case, one or more component carriers are aggregated to support a broad bandwidth. For example, if one component carrier supports a bandwidth of 5 MHz, 10 MHz or 20 MHz, maximum five component carriers are grouped to support a system bandwidth of maximum 100 MHz.
In a TDD system that supports such a carrier aggregation environment, if each uplink-downlink configuration is provided per carrier and cross carrier scheduling is performed, collision between a downlink of one carrier and an uplink of another carrier occurs, whereby a problem may occur in data transmission or reception.